1. Field of the Invention
The present invention relates to a coordinate detecting apparatus with a display unit of a type having a separated control unit and arranged in such a manner that the coordinate detecting apparatus with the display unit constituted by superposing a flat type display unit on a coordinate detecting unit is connected to a control unit disposed separably by a means of a cable. More particularly, the present invention relates to a coordinate detecting apparatus with a display unit of a type having a separated control unit having only one connection cable and thereby exhibiting improved handling facility.
2. Related Art Statement
Hitherto, an apparatus of the aforesaid type has been constituted by superposing a plate-like display unit for displaying the contents to be operated by the control unit in a real time manner on a coordinate detecting unit acting as an input unit for inputting data to the control unit. In the aforesaid apparatus, the position indicated by a coordinate indicator is detected, so that coordinate data or data about a handwritten character or the like formed into a numeral is transferred to the control unit via the cable. Furthermore, data about the contents to be displayed supplied from the control unit is received via a cable. An apparatus of this type is disclosed in detail in Japanese Patent Laid-Open No. 63-115218 titled "POSITION DETECTING APPARATUS" filed by the applicant of the present invention.
FIG. 15 is a perspective view of the components of a typical conventional coordinate detecting apparatus with a display unit of a type having a separated control unit. A coordinate detecting apparatus or tablet 51 with a display unit is mainly composed of a coordinate detecting unit disposed in a frame 56 and a display unit 55 superposed on the coordinate detecting unit. In the conventional apparatus shown in FIG. 15, three cables connect the coordinate detecting apparatus 51 with the display unit. That is, a serial signal cable 57 for transmitting/receiving coordinate data or the like to and from a control unit 52 (hereinafter called a computer body, if necessary), a video signal cable 58 for transmitting/receiving data about the contents to be displayed to and from the computer body 52 and a power supply cable 59 through which power is supplied from a power supply unit 53 are connected to the coordinate detecting apparatus 51 with the display unit.
FIG. 16 is a block diagram of an essential portion of the apparatus shown in FIG. 15. The coordinate detecting apparatus 51 with the display unit is mainly composed by superposing the display unit 55 on a coordinate detecting unit 54. The conventional apparatus shown in FIG. 16 further includes a backlight 61 disposed on the reverse side of the display unit 55. Although the display unit 55 may comprise a plasma display or a so-called reflecting type liquid display each of which is not coupled with the backlight 61, the backlight 61 structure shown in FIG. 16 must be used in a case including a so-called transmission type liquid crystal display to attain brightness advantages.
The display unit 55 is controlled by a display unit control means 62 disposed in the frame 56 of the coordinate detecting apparatus 51 with the display unit. The coordinate detecting unit 54 is controlled by a detecting unit control means 64 also disposed in the frame 56. A power supply circuit 63 supplies power required to operate the backlight 61, the display unit control means 62, and the detecting unit control means 64, and the like. The power supply unit 53 converts a domestic 100 or 200 V AC a DC level of about 10 V supplied to the power supply circuit 63 via a power supply cable 59. The power supply circuit 63 converts the 10 volt DC level into proper driving voltage for each of the backlight 61, the display unit control means 62 and the detecting unit control means 64 so as to supply it to these elements.
A CRT control means 70 transfers a video signal representing displayed data to the display unit control means 62 via the video signal cable 58; the video signal is converted into a graphic control signal by the display unit control means 62. As a result, data about the contents to be displayed are displayed on the display unit 55. The display unit control means 62 is connected to the CRT control means 70 in the computer body 52 via the video signal cable 58 so as to transmit/receive the signal which denotes the contents to be displayed. The detecting unit control means 64 is connected via the serial signal cable 57, to a serial signal control means 71 disposed in the computer body 52 so as to transmit/receive a signal which denotes coordinate data or the like.
The computer body 52 comprises a CPU 65 and a bus 68 connected to the CPU 65, the computer body 52 further comprising a ROM 66, a RAM 67, the CRT control means 70 and the serial signal control means 71 respectively connected to the bus 68. The power required for each of the aforesaid circuits is derived from a power source 69. The power source 69 is a power supply means provided independently from the power supply unit 53. In this description, the "CPU" is a central processing unit, the "ROM" is a read only memory memorizing a control program for controlling this apparatus and the like, the "RAM" is a random access memory which stores coordinate data transferred from the coordinate detecting apparatus 51 associated with the display unit and the like and the "CRT" is a display unit having a so-called cathode-ray tube.
Since the conventional coordinate detecting apparatus with the display unit has three cables connected thereto, the aforesaid cables deteriorate the handling facility of the apparatus. That is, there arises a problem in terms of the handling facility at the time of the data input operation and the transportation of the apparatus.
Furthermore, since a relatively high transferring frequency is used in a case where the video signal is employed to transfer data, a countermeasure must be taken against generation of noise affecting the environment.
Another problem arises in that there is an excessive limit in designing the display unit control means such as a liquid crystal controller for receiving a video signal and controlling the display unit as compared with a case where it is directly connected to the bus of the computer body.